Invar forming method for making tooling

ABSTRACT

A method for fabricating an Invar tool includes the step of superplastically forming an Invar facesheet for the tool. A tool header is provided, and the Invar facesheet is then formed with an SPF diaphragm driver to match the predetermined contour of the tool header. The Invar facesheet is then welded to the tool header. Forming the Invar facesheet is achieved by positioning the Invar facesheet between a superplastically formable diaphragm and a die having the predetermined contour. The diaphragm is heated to a predetermined superplastic temperature, and a predetermined pressure is applied to the diaphragm. Application of the predetermined pressure allows the diaphragm to cause the Invar facesheet to form against the predetermined contour of the die. Superplastically forming the Invar facesheet results in a negligible amount of excess scrap, reduces material costs, and reduces labor costs.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. patent application No.09/528,328 filed on Mar. 20, 2000, presently allowed.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention relates generally to Invar toolfabrication. More particularly, the invention relates to a method forfabricating an Invar tool including the step of superplastically formingan Invar facesheet to match or to approximate a predetermined contour ofthe tool.

[0004] 2. Background Art

[0005] Modern day aerospace, defense, and high tech researchapplications typically require complex, high precision, and closetolerance tooling. Thermal expansion is an area of particular concern inthe aerospace industry with regard to tooling. For example, mostmilitary aircraft applications stipulate that tools exhibit minimaldimensional changes when subjected to extreme temperature variations.

[0006] In the campaign to control thermal expansion, a useful materialhas been developed under the tradename of Invar 36. Invar 36 (“Invar”)is a nickel-iron alloy that has a rate of thermal expansion that isapproximately one-tenth that of carbon steel at temperatures up to 400degrees F. Invar therefore has a particular attractiveness infabricating tool components, including a header, which serves as a“frame” for a tool, and a facesheet, which is welded to the header.

[0007] Several of our first approaches in developing the presentinvention were labor and material intensive. One such approach involveda stretch forming technique as shown in FIGS. 3 and 4. Specifically, astretch form die was fabricated to a predetermined contour, and theInvar facesheet was stretched over the die surface. We considered thisforming process to be unsuccessful as it required a substantial amountof excess Invar material for the jaws of the stretch press which areused to grip the facesheet. As the amount of this excess Invar materialwas typically equal to the amount of material that was required to makethe facesheet, and as the excess material could not be used as the partof the tool, the excess Invar material needed to be trimmed, which ledto substantial waste. Another one of our approaches involved bumpforming thick Invar material, and cutting the material to fit the toolin segments. Yet another one of our approaches included the use ofcastings. This approach, however, was very expensive due to the need toeliminate porosity. It is therefore desirable to provide a method andassembly for fabricating an Invar tool with reduced labor and materialcosts.

SUMMARY OF THE INVENTION

[0008] A preferred method of the present invention for fabricating anInvar tool includes the step of providing a tool header defining apredetermined contour. An Invar facesheet is then superplasticallyformed to match, accurately or substantially, the predetermined contourof the tool header. Normally, the method further provides for weldingthe Invar facesheet to the tool header. Forming the Invar facesheet inthis way results in less scrap, and therefore substantially reducesmaterial costs. Forming the Invar facesheet in this way also leads toreduced labor costs.

[0009] The present invention further provides an Invar tool. The Invartool includes a tool header defining a predetermined contour, and one ormore Invar facesheets welded to the tool header. The Invar facesheetsare formed with an SPF diaphragm driver to substantially match thepredetermined contour of the tool header.

[0010] Further in accordance with the present invention, a method formolding parts on Invar tooling is provided. The method includes the stepof making an Invar tooling surface from a sheet of Invar with SPFdiaphragm forming. The sheet is placed on a tool header, and a part isformed against or on the tooling surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The various advantages of the present invention will becomeapparent to one skilled in the art by reading the followingspecification and sub-joined claims and by referencing the followingdrawings in which:

[0012]FIG. 1 is a perspective view of an Invar tool fabricated inaccordance with the present invention;

[0013]FIG. 2 is a perspective view of a superplastically formed Invarfacesheet in accordance with the present invention;

[0014]FIG. 3 is a perspective view of an Invar tool fabricated inaccordance with one of our first approaches in developing the presentinvention;

[0015]FIG. 4 is a perspective view of an Invar facesheet formed inaccordance with one of our first approaches in developing the presentinvention;

[0016]FIG. 5 is an exploded perspective view of a superplastic formingassembly in accordance with the present invention;

[0017]FIG. 6a is a cross-sectional side view taken along lines 6-6 inFIG. 5 of a superplastic forming assembly before fabrication inaccordance with the present invention;

[0018]FIG. 6b is a cross-sectional side view taken along lines 6-6 inFIG. 5 of a superplastic forming assembly during fabrication inaccordance with the present invention;

[0019]FIG. 6c is a cross-sectional side view taken along lines 6-6 inFIG. 5 of a superplastic forming assembly after fabrication inaccordance with the present invention;

[0020]FIG. 7 is an enlarged side view of area A shown in FIG. 6c;

[0021]FIG. 8 is a cross-sectional side view taken along lines 8-8 inFIG. 5 of a superplastic forming assembly in accordance with the presentinvention;

[0022]FIG. 9 is a perspective view of a mold for a ceramic die inaccordance with the present invention;

[0023]FIG. 10 is a side view of a process for pouring a ceramic castablematerial into the mold shown in FIG. 9; and

[0024]FIG. 11 is a perspective view of a ceramic die loaded onto a pressbed in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Referring to FIGS. 1 and 2, an Invar tool 20 fabricated inaccordance with the principles of the present invention includes a toolheader 21 having a predetermined contour and an Invar facesheet 22.Invar facesheets 22 are preferably superplastically formed in adiaphragm forming process using an SPF alloy driver to match thepredetermined final contour in segments. The segments are welded to thetool header 21 to define the forming surface of the tool and to completethe tool with minimal waste of the Invar.

[0026]FIG. 5 shows a preferred superplastic forming assembly 40 of thepresent invention. The preferred superplastic forming (SPF) assembly 40includes a press bed 41, and a die 42 coupled to the press bed 41. Thedie 42 has a predetermined contour corresponding to the Invar tool 20(FIG. 1). The SPF assembly 40 further includes a superplasticallyformable diaphragm 43, and a sealing ring 44 positioned between the die42 and the diaphragm 43. A press head 45 is coupled to the diaphragm 43.The press head 45 has an associated head weight, and applies apredetermined pressure to the diaphragm 43 such that the Invar facesheet22 forms against the predetermined contour of the die 42. It will beappreciated that the head weight is sufficient to offset the reactiveforce of the predetermined pressure. Further details of a suitable SPFpress are described in U.S. Pat. No. 5,467,626.

[0027]FIGS. 6a-6 c demonstrate the process of forming the Invarfacesheet 22 in greater detail. Specifically, the Invar facesheet 22 ispositioned between the diaphragm 43 and the die 42 having thepredetermined contour 46. The diaphragm 43 is a superplastic alloy, suchas titanium. It is heated to a predetermined superplastic temperature,and a predetermined pressure is applied to the diaphragm 43 such thatthe diaphragm 43 causes the Invar facesheet 22 to form against thepredetermined contour 46 of the die 42. The Invar facesheet softens atthe SPF temperature, allowing it to be stretched with the diaphragm. Inone embodiment, the diaphragm 43 includes titanium, and thepredetermined pressure is applied via argon gas. Superplasticallyforming the Invar facesheet 22 allows the Invar facesheet 22 to beprofiled to accommodate the predetermined contour 46 before forming andresults in a substantial reduction in material waste. An importantaspect of the SPF process involves proper forming of the die 42 to allowunrestricted fabrication of the Invar facesheet 22.

[0028] Thus, the Invar facesheet 22 transitions from a flat shape asshown in FIG. 6a, to a partially formed shape as shown in FIG. 6b, to afinally formed shape as shown in FIG. 6c. It is also important to notethat as shown in FIG. 8, the Invar facesheet 22 can be formed inmultiple directions as dictated by the predetermined contour 46. Thisincreased ability to customize the Invar facesheet is highly desirableover conventional stretch forming approaches to Invar tool fabrication.

[0029]FIG. 7 shows that the sealing ring 44 undergoes compression inresponse to the head weight of the press head 45. The sealing ring 44 ispreferably made of stainless steel and adds stability to the overall SPFprocess.

[0030] It is preferred that the die 42 be formed from a ceramic castablematerial, as described in U.S. Pat. No. 5,467,626. Thus, as shown inFIG. 9, the process of forming the die 42 includes the step of creatinga mold 50 having the predetermined contour 46. FIG. 10 demonstrates thatthe ceramic castable material 51 is poured into the mold 50. The ceramiccastable material 51 is then allowed to set into the ceramic die 42, andthe ceramic die 42 is demolded. As shown in FIG. 11, the ceramic die 42is cured at the predetermined superplastic temperature, and loaded ontothe press bed 41. In one embodiment, the predetermined superplastictemperature is approximately 1650 degrees F., and the predeterminedpressure of the argon gas is approximately 90-180 psi. Curing theceramic die 42 at the predetermined superplastic temperature insuresthat the ceramic die 42 will not undergo undesirable thermal expansionduring the SPF process.

[0031] Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the present invention can beimplemented in a variety of forms. Therefore, while this invention hasbeen described in connection with particular examples thereof, the truescope of the invention should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, specification and the following claims.

1. A method of forming a part on Invar tooling, the method comprising:using a tool header having a surface with a desired curvature to providea support surface; placing an Invar facesheet with a preformed contourat least substantially in accordance with said desired curvature of saidtool header surface, against said tool header surface; securing saidInvar facesheet to said tool header surface such that said Invarfacesheet and said tool header cooperatively form an Invar tool; andusing said Invar tool to as a support surface to help form said partinto a desired shape.
 2. The method of claim 1, wherein placing saidInvar facesheet against said tool header surface comprises placing anInvar 36 facesheet against said tool header surface.
 3. The method ofclaim 1, wherein placing said Invar facesheet against said tool headersurface comprises placing a superplastically formed (SPF) Invarfacesheet against said tool header surface.
 4. The method of claim 1,further comprising placing a plurality of Invar facesheets each having apredetermined curvature against said tool header surface.
 5. The methodof claim 1, further comprising securing said Invar facesheet to saidtool header surface by welding.
 6. A method of forming a part using anInvar tool, the method comprising: using a tool header having a surfacewith a desired curvature to provide a support surface; placing at leastone Invar facesheet with a preformed contour at least substantially inaccordance with said desired curvature of said tool header surface,against said tool header surface; fixedly securing said Invar facesheetto said tool header surface to form a unitary Invar tool; and using saidInvar tool as a support surface to help impart a desired shape to a partplaced against said Invar tool and forcibly urged against said Invartool.
 7. The method of claim 6, further comprising welding said Invarfacesheet to said tool header surface.
 8. The method of claim 6, whereinplacing at least one Invar facesheet comprises placing at least oneInvar 36 facesheet against said tool header surface.
 9. The method ofclaim 6, wherein placing at least one Invar facesheet comprises placingat least on superplastically formed (SPF) Invar facesheet against saidtool header surface.
 10. A method of forming a part with a desiredcurvature, comprising: using a tool header having a surface with adesired shape to provide a support surface for supporting said part;placing a superplastically formed (SPF) Invar facesheet with a preformedcontour at least substantially in accordance with said desired shape ofsaid tool header surface, against said tool header surface, tosubstantially cover said surface of said tool header; fixedly securingsaid Invar facesheet to said tool header surface such that said Invarfacesheet and said tool header surface are held immovably relative toone another, and such that said Invar facesheet and said tool headercooperatively form an Invar tool; and using said Invar tool to as asupport surface to help form said part into a desired shape when saidpart is urged against said Invar tool.
 11. The method of claim 10,wherein fixedly securing said Invar facesheet comprises welding saidInvar facesheet to said tool header surface.
 12. The method of claim 10,wherein placing said SPF Invar facesheet against said tool headersurface comprises placing a SPF Invar 36 facesheet against said toolheader surface.